The invention relates to a hybrid vehicle including a combustion engine having a driveshaft for propelling the wheels of at least one axle, at least one electrical machine for propelling the wheels of this one or at least one further axle, with the at least one electrical machine capable of being operated during a braking operation as a generator and during an acceleration operation as a motor, and a further electrical machine coupled with the at least one electrical machine and having a flywheel store which includes a rotor and which can be charged during a braking operation and discharged during an acceleration operation.
The use of flywheels in vehicles has long been known. DE 639 717 A proposes the provision of a flywheel store for vehicles, with a shiftable transmission being arranged between the flywheel and the drive train of a vehicle. Instead of a mechanical range-change transmission, the use of an electrical gearbox is also possible.
AT 147 860 B discloses a flywheel store for motor vehicles. A combustion engine drives an axle as main propulsion; the flywheel store drives one or more additional drive axles.
DE 10 2010 007 632 A1 proposes a hybrid vehicle having a combustion engine for driving the rear axle, and two electrical machines at the front axle. The electrical machines are operated during braking operation as a generator to recover kinetic energy. The energy gained during recuperation is supplied to a flywheel intended as energy store. For this purpose, current which is generated by the electrical machine arranged on the front axle is fed to a third electrical machine which is arranged in the flywheel store so as to cause movement of a rotor of the flywheel store. This rotor can reach rotation speeds up to 40,000 1/min. The rotor provided in the hybrid vehicle is used as a mechanical energy storage so that the need for an electrochemical storage battery, like in other conventional hybrid vehicles, is eliminated. Following a braking operation, the recovered energy stored in the form of kinetic energy is available for an acceleration process. For that purpose, the third electrical machine of the flywheel store is operated as a generator, thereby producing electrical energy while slowing down the rotor, which electrical energy in turn is fed to the first and second electrical machines at the front axle. This electrical energy acts as additional driving energy to assist the combustion engine which drives the rear axle.
In order to improve efficiency and controllability, hybrid vehicles typically use an electric gearbox with at least one electrical machine or a CVT transmission (continuously variable transmission). However, both the electric gearbox and the CVT lead to a high system weight, when the power being transmitted is high. Therefore, only a limited proportion of the braking energy that actually occurs can be converted into kinetic energy. The major proportion of the braking energy is still wasted as heat. Many vehicles, such as buses, sanitation trucks or delivery vehicles are, however, operated to frequently decelerate and accelerate again. The same applies to motor sport vehicles and in general to vehicles in urban traffic.